1. Field of the Invention
The invention relates in general to a differential-to-single-end converter, and more particularly to a converter that converts a differential input signal to a single-end output signal.
2. Description of the Related Art
To withstand noises from power lines and a semiconductor substrate, internal signals of an integrated circuit may be processed by a differential mode. For example, a ring oscillator often generates clock signals by a differential mode to prevent common mode noises from affecting the frequency.
However, a differential signal in the differential mode requires at least two signal transmission lines. Compared to one signal transmission line that a single-end signal requires, the design of the at least two signal transmission lines increases routing complexities and a pin count in an integrated circuit. As a result, signals of most logic circuits in an integrated circuits adopt the single-end mode, and only signals that demand a high noise resistance adopt the differential mode. A differential-to-single-end converter converts a differential input signal to a single-end output signal, and serves as a bridge between circuits of different signal modes.
Referring to FIG. 1, a conventional differential-to-single-end (D2S) converter 10 includes two NMOS transistors N1 and N2, and two PMOS transistors P1 and P2. The differential-to-single-end converter 10 may be regarded as a conventional differential amplifier. A non-inverted signal S-NON and an inverted signal S-INV that form a differential signal are respectively inputted at gates of the NMOS transistors N1 and N2. The PMOS transistors P1 and P2 form a current mirror, and have a common control node CON-O that connects to a drain of the PMOS transistor P1. The NMOS transistor N1 and the PMOS transistor P1 are connected in series between power lines VDD and VSS. The NMOS transistor N2 and the PMOS transistor P2 are connected in series between power lines VDD and VSS via an output node OUT. The output node OUT generates a single-end signal S-ONE.
A good differential-to-single-end converter is capable of quickly changing a logic value of its single-end signal as a logic value of a differential signal switches. Further, the differential-to-single-end converter also needs to a have a fast voltage slew rate. As such, when a differential clock signal provided by a ring oscillator is received to generate a single-end clock signal, a duty cycle of the single-end clock signal may approximate an ideal value of 50%.